The battle between sports cheats and testers is poised to enter a whole new arena. The World Anti-Doping Agency has extended its 2003 ban on “gene doping” to include all forms of gene editing – but it is not clear the agency has the means to enforce this ban.

WADA already bans the use of genetically modified cells and gene therapy if they have “the potential to enhance sport performance”. From 2018, the list will also include “gene editing agents designed to alter genome sequences and/or the transcriptional or epigenetic regulation of gene expression”.

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Gene editing should be even harder to detect than conventional gene therapies like this. Gene editing should make it possible to make tiny alterations to DNA in existing genes, or to just temporarily boost or switch off the activity of particular genes. What’s more, these tweaks can be restricted to specific tissues such as muscle, meaning the changes may not show up in blood tests.

In theory, the “biological passports” introduced by WADA in 2009 should reveal any unexpected changes in an athlete’s body, even if gene doping itself cannot be detected. But any would-be cheats smart enough to resort to gene editing may be able to find ways round this.